The present invention generally relates to an apparatus and a method for detecting a flammable gas in a gas mixture and more particularly, relates to an apparatus and a method for detecting a flammable gas in an exhaust gas flown from a process machine by utilizing an ignitor and a temperature sensor for igniting the flammable gas in a reactor chamber and then sensing a temperature rise caused by the ignition of the flammable gas so that the exhaust gas flow may be shut-off.
In the fabrication of semiconductor devices, a semi-conducting wafer must be processed in a large number of processing steps for producing integrated circuit chips. These processing steps may amount to as many as several hundred. The various processing steps are conducted in a variety of processing machines to carry out various chemical or physical reactions on the semi-conducting wafer. In the various fabrication steps an effluent or exhaust gas from the process machine must be treated either in a chemical reaction process or in an absorption or condensation process before it can be released into a factory exhaust system and subsequently into the atmosphere. A large number of reactant gases and their reaction products utilized in the semiconductor fabrication industry are highly flammable or highly toxic. The gases exhausted out of a process chamber may include gases that have not been reacted or have been partially reacted and therefore, must be treated before they can be released into the factory exhaust system or into the atmosphere.
Exhaust gas treatment systems have been used for converting toxic gases into nontoxic substances. One of such gas treatment systems is a gas reactor column (GRC) designed to eliminate hazardous gases from the exhaust of semiconductor process chambers. A gas reactor column may be a hot-bed type reactor that treats a variety of gases in a single cartridge without creating additional effluent disposal problems. These types of gas reactor columns, while efficient in converting toxic gases into non-toxic gases, are not particularly useful in treating flammable gas components in an exhaust gas mixture.
Another method of treating exhaust gases is the use of an absorption unit which functions on the principle of gas absorption into a porous substance without chemical reactions taking place. This type of physical absorption process can be carried out by using a bed of porous substance such as activated carbon for absorbing certain components in exhaust gases, specifically those of low boiling temperature and of foul-smelling. While the low boiling temperature gases, i.e., those having a boiling temperature of less than 100xc2x0 C., can be successfully removed by an absorption apparatus filled with a substance such as activated carbon, the high boiling temperature gases, i.e., those are likely flammable, cannot be effectively removed by the absorption apparatus.
Still other methods combines a conventional absorption method and a conventional condensation method. For instance, one of such apparatus for carrying out a combined absorption/condensation method is shown in FIG. 1. Apparatus 10, shown in FIG. 1, utilizes an absorption apparatus for absorbing the low boiling temperature gases in an exhaust gas mixture and a condensation apparatus for condensing the high boiling temperature components in the exhaust gas mixture. For instance, the dual-stage apparatus 10 for treating an exhaust gas from a semiconductor fabrication machine consists of a condensation unit 20 and an absorption unit 30. Exhaust gas 12 from a fabrication machine is fed through a flow control valve 14, a filter 16 into a condenser 28 which is part of the condensing unit 20. The condensing unit 20 consists of the condenser 28, a liquid collection tank 32 and a pump 34. The liquid collection tank 32 collects the condensed liquid from condenser 28 through pipe 36 and pumps it away by pump 34. A city water supply 38 may be used, either with or without refrigeration, as the cooling water in condenser 28. Normally high boiling temperature components of the exhaust gas 12 are removed by the condensing unit 20. However, for high boiling temperature gases such as BMOS (C2H6SO) and NMP (C3H9NO), the efficiency of removal by the condensing unit 20 is less than 70%.
At the output end of the condensing unit 20, partially treated exhaust gas 42 exits and is fed into an absorption unit 30. The absorption unit 30 is constructed of an absorption bed 52 which contains a porous material such as activated carbon, or any other suitable porous material. The inlet and the outlet pressure of the absorption bed 52 is monitored by a differential pressure gauge 54. The monitoring of the differential pressure is important since it provides an indication when the absorption medium, i.e., the activated carbon, needs to be replaced or replenished. The exhaust gas 58 exiting the absorption bed 52 is taken away by a blower 62 and fed into a factory exhaust system for releasing to the atmosphere.
The conventional exhaust gas treatment system 10 of FIG. 1 is not efficient in removing the high boiling temperature components, i.e., the high flammability gases, in the exhaust gas mixture. This presents a serious problem in that not only the high boiling temperature gases pollute the environment when released to the atmosphere, the high flammability gases also create a serious fire or explosion hazard in the factory exhaust system. When an explosion or fire occurs in the factory exhaust system, fire propagates to all process machines that are connected in fluid communication with the factory exhaust line. The potential fire hazard can therefore cause destruction of an entire fabrication facility when the factory exhaust line is connected to a large number of process chambers.
It is therefore an object of the present invention to provide an apparatus capable of detecting flammable gas components in a gas mixture exhausted from a semiconductor fabrication machine so that the flammable gas components may be prevented from entering a factory exhaust system.
It is another object of the present invention to provide a method for detecting the flammable gas components in a gas mixture exhausted from a semiconductor fabrication machine and for preventing the flammable gas components from entering a factory exhaust system.
It is a further object of the present invention to provide an apparatus for detecting flammable gas components in a gas mixture by utilizing a reactor chamber in which the flammable gas components may be ignited.
It is another further object of the present invention to provide an apparatus for detecting flammable gas components in a gas mixture by using a reactor chamber equipped with an electronic ignitor and a temperature sensor.
It is still another object of the present invention to provide an apparatus for detecting a flammable gas in a gas mixture by utilizing a reactor chamber equipped with an electronic ignitor, a temperature sensor and a valve means for shutting off the supply of the flammable gas when the temperature sensor senses a temperature rise.
It is yet another object of the present invention to provide an apparatus for detecting a flammable gas in a gas mixture by utilizing a reactor chamber equipped with an electronic ignitor, a temperature sensor and a two-way solenoid valve capable of switching an input to the reactor chamber from an exhaust gas to ambient air.
It is still another further object of the present invention to provide a method for detecting a flammable gas in a gas mixture by igniting the flammable gas in a reactor chamber and detecting a temperature rise of the gas mixture.
It is yet another further object of the present invention to provide a method for detecting a flammable gas in a gas mixture by igniting in a reactor chamber the flammable gas and detecting a temperature rise of more than 30xc2x0 C. such that an input to the reactor chamber can be switched to ambient air by a two-way solenoid valve.
In accordance with the present invention, an apparatus and a method for detecting a flammable gas in a gas mixture are provided.
In a preferred embodiment, an apparatus for detecting a flammable gas in a gas mixture is provided which includes a chamber that has an inlet, an outlet and a cavity contained therein, the cavity is equipped with an ignitor means and a temperature sensor, an air pump which has an inlet connected to the outlet of the chamber such that the inlet of the air pump is in fluid communication with the inlet of the chamber enabling a gas mixture flowing therethrough at a speed of not less than 5 meter/second, and a valve means for shutting off the inlet to the chamber when the ignitor means ignites a flammable gas in the gas mixture and the temperature sensor senses a temperature rise of at least 10xc2x0 C.
The valve means in the apparatus for shutting off the inlet to the chamber may be a solenoid valve, or a two-way solenoid valve for switching between a gas mixture supply and an ambient air supply. The apparatus may further include a flow meter situated in-between and in fluid communication with the valve means and the chamber for measuring a flow rate of the gas mixture. The air pump enables a gas mixture to flow therethrough at a speed of not less than 5 meter/second, and preferably at a speed of not less than 10 meter/second. The valve means may shut-off the gas mixture when a flow speed of the mixture is measured at less than 5 meter/second. The valve means may also shut-off the gas mixture when a malfunction of the ignitor means is detected. The gas mixture flowing through the inlet to the chamber may be an exhaust gas from a semiconductor process chamber. The apparatus may further include a solenoid valve and a flow meter.
The present invention is further directed to a method for detecting a flammable gas in a gas mixture which can be carried out by the operating steps of first providing a reactor chamber that has an inlet, an outlet and a cavity contained therein, then positioning an ignitor means and a temperature sensor in the cavity, then flowing a gas mixture through the inlet of the reactor chamber into the cavity and igniting the gas mixture by the ignitor means, and stopping the flow of gas mixture when the temperature sensor detects a temperature rise in the cavity.
The method may further include the step of flowing the gas mixture through a flow meter prior to entering the inlet of the reactor chamber. The method may further include the step of igniting the gas mixture by an electronic ignition means. The method may further include the step of stopping the gas mixture flow by a solenoid valve and flowing ambient air into the cavity of the reactor chamber when the temperature sensor detects a temperature rise in the cavity. The method may further include the step of flowing a gas mixture containing a flammable gas into the cavity and igniting the flammable gas by the ignitor means. The method may further include the step of stopping the gas mixture flow when the temperature sensor detects a temperature rise of more than 10xc2x0 C.
The method for detecting a flammable gas in a gas mixture may further include the step of stopping the gas mixture flow in a time period of less than 0.5 second when the temperature sensor detects a temperature rise. The method may further include the step of stopping the gas mixture flow when a flow speed of the gas mixture flow is measured at not more than 5 meter/second. The method may further include the step of stopping the gas mixture flow when a malfunction of the ignitor means is detected. The method may further include the step of flowing a gas mixture through an inlet of the reactor chamber by withdrawing from an outlet of the reactor chamber with a pump capable of producing a flow speed of at least 5 meter/second.
In another preferred embodiment, the present invention provides an apparatus for detecting a flammable gas in a gas mixture by pyrolysis which includes a reactor chamber equipped with a gas inlet, a gas outlet, an ignitor means and a temperature sensor, a gas evacuation means in fluid communication with the gas outlet of the reactor chamber capable of withdrawing a gas mixture containing a flammable gas from the chamber at a flow speed of at least 5 meter/second. A solenoid valve for switching between a gas mixture source and an ambient air source, a flow meter positioned in-between of and in fluid communication with the solenoid valve and the gas inlet on the reactor chamber for detecting the flow speed, and a controller for switching the solenoid valve from the gas mixture source to the ambient air source when a flammable gas is ignited in the reactor chamber and a temperature rise is detected by the temperature sensor.
The apparatus may further include a reactor chamber equipped with an electronic ignition means. The gas evacuation means may be an air pump that is capable of withdrawing the gas mixture containing a flammable gas from the reactor chamber at a flow speed of between about 5 meter/second and about 25 meter/second. The solenoid valve may be a two-way solenoid valve operated by a mechanical spring. The temperature rise detected by the temperature sensor is at least 10xc2x0 C., and preferably at least 30xc2x0 C. The controller is capable of switching the solenoid valve from the gas mixture source to the ambient air source when a flammable gas is ignited in a time period of not more than 0.5 second. The controller may also switch the solenoid valve from the gas mixture source to the ambient air source when a flow speed of less than 5 meter/second is detected by the flow meter. The controller may further switch the solenoid valve from the gas mixture source to the ambient air source when a malfunction of the ignitor means is detected. The gas mixture which contains a flammable gas may be an exhaust gas from a semiconductor process chamber.